In general, work machines such as a hydraulic excavator are provided with various kinds of fluid pressure actuators which are operated by pressurized fluid from pumps, and there has conventionally been known a technique for regenerating the energy of fluid discharged from the fluid pressure actuators such as a technique in which the pressure of fluid discharged from each fluid pressure actuator is recovered to be accumulated in an accumulator. However, accumulators result in problems in that they require a large capacity relative to the energy storage amount in comparison with other energy storage means such as batteries, and further that they have shorter storage times.
There is thus a need for improved techniques for regenerating and storing the energy of fluid discharged from a fluid pressure actuator as electrical energy.
Work machines such as a hydraulic excavator are generally arranged in such a manner that the flow rate of fluid discharged from a fluid pressure actuator is controlled by a control valve which performs meter-out control based on the amount of throttle. In one known example, the technique disclosed in Japanese Published Unexamined Patent Application No. 2002-195218 provides a turbine, which is driven rotationally by the inflow of discharge fluid, on the downstream side of such a control valve. Therefore, before the turbine is rotated to regenerate energy, the control valve removes the discharge fluid from the fluid pressure actuator, resulting in a temperature increase which thereby consumes energy, resulting in a problem of lower energy regeneration efficiency.
Further, although there is no consideration in Japanese Published Unexamined Patent Application No. 2002-195218 for the case that the fluid pressure actuator is a fluid pressure motor, various kinds of fluid pressure motors such as a hydraulic rotating motor for rotating an upper rotating body and/or a hydraulic traveling motor can be included in work machines such as a hydraulic excavator. Such fluid pressure motors generally include a control valve for flow rate control and a relief valve for preventing a pressure increase of a fluid supply flow path and/or a discharge flow path when starting or stopping the motor. The temperature of fluid passing through the relief valve can be increased to consume energy where there are demands that the energy of fluid passing through the relief valve could also be regenerated.
The present disclosure is aimed at solving this and other problems known to those skilled in the art.